1. Field of the Invention
The present invention generally relates to a metallization process for manufacturing semiconductor devices. More particularly, the present invention relates to preventing copper dewetting by depositing a transition metal that helps preserve the copper crystal structure and promote adhesion between copper and other materials.
2. Description of the Related Art
Copper is the current metal of choice for use in multilevel metallization processes that are crucial to semiconductor device manufacturing. The multilevel interconnects that drive the manufacturing processes require planarization of high aspect ratio apertures including contacts, vias, lines, and other features. Filling the features without creating voids or deforming the feature geometry is more difficult when the features have higher aspect ratios. Reliable formation of interconnects is also more difficult as manufacturers strive to increase circuit density and quality.
As the use of copper has permeated the marketplace because of its relative low cost and processing properties, semiconductor manufacturers continue to look for ways to improve the boundary regions between copper and dielectric material by reducing copper diffusion and dewetting. Several processing methods have been developed to manufacture copper interconnects as feature sizes have decreased. Each processing method may increase the likelihood of errors such as copper diffusion across boundary regions, copper crystalline structure deformation, and dewetting. Physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), chemical mechanical polishing (CMP), electrochemical plating (ECP), electrochemical mechanical polishing (ECMP), and other methods of depositing and removing copper layers utilize mechanical, electrical, or chemical methods to manipulate the copper that forms the interconnects. Barrier and capping layers may be deposited to contain the copper.
In the past, a layer of tantalum, tantalum nitride, or copper alloy with tin, aluminum, or magnesium was used to provide a barrier layer or an adhesion promoter between copper and other materials. These options are costly or only partially effective or both. As the copper atoms along the boundary regions experience changes in temperature, pressure, atmospheric conditions, or other process variables common during multiple step semiconductor processing, the copper may migrate along the boundary regions and become agglomerated copper. The copper may also be less uniformly dispersed along the boundary regions and become dewetted copper. These changes in the boundary region include stress migration and electromigration of the copper atoms. The stress migration and electromigration of copper across the dielectric layers or other structures increases the resistitivity of the resulting structures and reduces the reliability of the resulting devices.
Preventing agglomeration of copper, especially when seed layers of copper are deposited on dielectric or other materials, is a research goal. Reducing deviation from ideal copper crystalline structure and discouraging copper dewetting is important. Finally, it is desirable to decrease the likelihood of diffusion of copper into dielectric, barrier, or other layers.